Rare Martian meteorological phenomena have been found in pictures of Mars taken by the Viking Orbiter 1 spacecraft, managed for NASA by the Jet Propulsion Laboratory, Pasadena, Calif.

Weather activity never before observed on Mars was discovered in images taken on an exceptionally clear Martian day on Feb. 22, 1980.

Several prominent Martian features and at least two meterological anomalies are visible in mosaic of 102 frames taken that day. The photo-mosaic is probably the best wide area view of the Mars surface yet obtained.

The most remarkable weather activity in the mosaic appears as sharp, dark line which curves north and east from the huge volcano Arsia Mons in the Tharsis Ridge. Scientists believe this line is either weather front or atmospheric shock wave. Nothing like this weather phenomenon has ever been seen before on Mars.

The second unusual weather activity consists of four small clouds that hover just north of the Lowell crater. Though two of the clouds are so close together as to be almost inseparable even in high enlargement, four clearly separate cloud shadows are cast on the planet surface. The largest cloud is about 32 kilometers (20 miles) in length.

Judging from the distance between the clouds and shadows, the clouds float at an altitude of nearly 28 kilometers (91,000 feet). The shadows, which are cast to the south of the clouds, indicate that the photographs near the center of the mosaic were taken close to noon, local Martian time. Distinct cloud pattern shadows are rarely apparent on the face of Mars.

Viking Orbiter 1, which entered Mars orbit June 19, 1976, is nearing the end of four years of planetary operations, but continues to transmit an average of 30 pictures day to mission control at the Jet Propulsion Laboratory.

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This mosaic of 102 photos of Mars was taken Feb. 22, 1980, by Viking Orbiter 1. Several prominent Martian features and at least two rare weather phenomena are visible. Valles Marineris, as long as the North American continent from coast coast, stretches across the center. Three huge volcanoes of the Tharsis Ridge are at left: Arsia Mons, Pavonis Mons and Ascraeus Mons (from south to north). sharp line, either weather front or an atmospheric shock wave, curves north and east from Arsia Mons. This is the first time feature like this has been seen. Four tiny clouds can be seen in the southernmost frame, just north of large crater named Lowell. While the clouds are too close together to be resolved, even under high magnification, their shadows can be separated easily. The largest cloud is nearly 32 kilometers (20 miles) long. Measurements show the clouds' elevation as nearly 28 kilometers (9l,000 feet). Such distinct cloud shadow patterns are extremely rare on Mars. Viking Orbiter 1 has operated at Mars for almost four years and is nearing the end of its operational life. It continues to send about 30 pictures day to controllers at Jet Propulsion Laboratory.